One of the main areas of emphasis in this research has been the relationship between photoreceptors and pigment epithelium in the vertebrate retina. The cyclic shedding of photoreceptor membrane by rods and cones and its phagocytosis by pigment epithelial cells has been examined in the tree squirrel retina and is being examined in the domestic cat. In the tree squirrel there is a peak of disc shedding from photoreceptors at about 1 hour after the onset of light and a second, small peak about 7 hours after the onset of darkness. Phagosomes arise from rods, and the p.m. peak from cones. Xenopus eye explants have been grown in vitro for up to 48 hours. When whole animals or the explants are exposed to 5 minutes of white light (550-650 lux) rod disc shedding increases significantly. The anatomical relationship between cat cones and pigment epithelium is being studied by transmission and scanning electron microscopy in both the adult and developing cat. The organization and development of the outer plexiform layer is being studied in the cat and human retina by light and electron microscopy.